Membrane separation technology is a novel high-efficiency and energy-saving separation technology that is widely used in many fields of petrochemical industry, food, medicine, energy, electronic industry, environmental protection and so on. As one of the high and new technologies for realizing sustainable economic development of China, membrane separation technology shows the significant advantage in solving the major problems as resource shortage, energy shortage and environmental pollution, etc. With the constant development in the field of membrane technology application, the requirement for the membrane material becomes more rigorous and the application scope of the organic polymeric membrane with low cost is limited to some extent. Therefore, the research and development for high-performance membrane materials that possess favorable thermal and chemical stability and service condition adaptability has attracted much attention. Wherein, the inorganic membrane material with the advantages of high temperature resistance, great mechanical strength and high chemical resistance is applied more and more extensively in the field of membrane technology.
As an important part of inorganic membrane materials, in addition to some common features of inorganic membrane, zeolite membrane possess well-regulated and uniform pore structure, thus it possesses excellent catalysis property and separation selectivity and has a broad application prospect in membrane separation, membrane catalysis and ion exchange, etc. The pore diameter of the zeolite membrane is generally less than 1 nm. The effective separation between different molecules can be realized based on molecular sieving or difference in adsorption. More and more zeolite membranes have been applied in the pervaporation separation, such as NaA, MFI and T-types zeolite membrane, and the research on NaA zeolite membrane is conducted most extensively.
NaA zeolite membrane has a strong hydrophilicity and its pore size is 0.42 nm which is larger than the dynamic diameter of water molecule (0.29 nm) and smaller than most organic molecules. Therefore, the membrane material exhibits an extremely high water permeation selectivity in dehydrations of organic solutions. At present, pervaporation dehydration units using NaA zeolite membranes have been introduced to industrial application successfully. The adopted support of NaA zeolite membrane is mainly single-channel tube configuration with a low flux and limited loading density (30-250 m2/m3); nevertheless, its high equipment cost obstacles its further industrialization process.
Compared with the conventional tubal supports, the wall of the single-channel ceramic hollow fiber is thin, thus reducing trans-membrane resistance and increasing the permeation flux of NaA zeolite membrane greatly. Therefore, for higher packing density and separation efficiency of the membrane module and a low production cost, the single-channel ceramic hollow fiber support is introduced for the preparation of NaA zeolite membrane. Xu et al. (Xu et al. Journal of Membrane Science, 2004, 229(1): 81-85) prepared NaA zeolite membrane on single-channel ceramic hollow fiber support in 2004, however the dense NaA zeolite membrane only can be obtained through three times of synthesis; Wang et al. (CN200910098234.3) synthetized NaA zeolite membrane on the single-channel aluminum oxide hollow fiber support by adopting the crystal seed coating method of dip coating—roll coating, and the permeation flux of which was maintained between 5.0-9.0 kg·m−2·h−1; in addition, Wang et al. (CN201210051366.2) adopted the method of adding adhesive for crystal seed coating and synthetized NaA zeolite membrane on the inner surface of single-channel hollow fiber through dynamic hydrothermal synthesis, and the permeation flux of the membrane was between 5.9-6.9 kg·m−2·h−1.
Although the property of the single-channel hollow fiber zeolite membrane is improved to some extent compared with the conventional tube-type zeolite membrane, it is easy to be broken and damaged during the process of equipping and use due to poor mechanical property. Hollow fiber module is bundling packed. The breakage of the single fiber in the packing will cause liquid leakage for the whole module and thus to reduce overall separation property of the hollow fiber module. Through optimizing the hollow fiber configuration, we successfully prepared a multi-channel ceramic hollow fiber with high mechanical property and applied for a patent for invention (CN2013102440942). Developing the hollow fiber zeolite membrane combined with high mechanical property and high flux on multi-channel hollow fiber is the key to promote the industrialized application process of hollow fiber zeolite membrane.